1. Field of the Invention
This invention relates to the field of antibiotic and antiparasitic therapy. In particular this invention contemplates administration of inhibitors of fatty acid synthesis or metabolism to patients suffering from microbial or parasitic infection or colonization.
2. Background Information
In lower organisms such as yeast and bacteria fatty acid synthesis differs from that in humans. In bacteria (prokaryotes) the actual assembly of fatty acids occurs by seven separate enzymes. These enzymes are freely dissociable and are classified as Type II synthases. Type II fatty acid synthases are specifically inhibited by the drug Thiolactomycin. Thiolactomycin, (4S)(2E,5E)-2,4,6-trimethyl-3-hydroxy-2,5,7-cotatriene-4-thiolide, is a unique antibiotic structure that inhibits dissociated, but not multifunctional fatty acid synthases. The antibiotic is not toxic to mice and affords significant protection against urinary tract and intraperitoneal bacterial infections.
In higher organisms however, gene fusion events have occurred among the seven separate enzymes from bacteria. This resulted in multifunctional enzymes for fatty acid synthesis which are classified as Type I. In yeast, such as S. cerevisiae, them are two distinct polypeptides designated as alpha and beta which are responsible for fatty acid synthesis. The major products of fatty acid synthesis in yeast are 16 and 18 carbon saturated fatty acids produced as coenzyme-A derivatives. In mycobacterium, such as M. smegmatis, all of the enzyme activities are on one large polypeptide of 290,000 Da. The product of this synthase are 16 to 24 carbon saturated fatty acids derivatized to coenzyme-A. In pathogenic Mycobacterium, such as Nocardia species, there exists a second synthase, mycocerosic acid synthase (MAS). This synthase is responsible for very long chain branched fatty acids. Importantly, MAS contains a beta-ketoacyl synthetase (condensing enzyme) activity similar to that of Type I fatty acid synthases.
While Thiolactomycin is a specific inhibitor of Type II fatty acid synthases, cerulenin is a specific inhibitor of Type I fatty acid synthases. Cerulenin was originally isolated as a potential antifungal antibiotic from the culture broth of Cephalosporium Caerulens. Structurally cerulenin has been characterized as 2R,3S-epoxy-4-oxo-7, 10-trans, trans-dodecanoic acid amide. Its mechanism of action has been shown to be inhibition, through irreversible binding, of beta-ketoacyl synthase, the condensing enzyme required for biosynthesis of fatty acids. Cerulenin has been categorized as an antifungal, primarily against Candida and Saccharomyces sp. In addition, some in vitro activity has been shown against some bacteria, antinomycetes, and mycobacteria, although no activity was found against Mycobacterium tuberculosis. The activity of fatty acid synthesis inhibitors and Cerulenin in particular has not been evaluated against protozoa such as Toxoplasma gondii or other infectious eucaryotic pathogens such as Pneumocystis carinii, Giardia lamblia, Plasmodium sp., Trichomonas baginalis, Crytosporidium, Trypanosoma, Leishmania, and Shistosoma.
Despite cerulenin's in vitro activity against some bacteria and fungi it has not been developed as a therapeutic agent. To date research on this compound has centered on its use as a research tool for investigating the role of fatty acids in the metabolism and physiology of a variety of organisms because of its activity as a fatty acid synthesis inhibitor.
The rational for the use of fatty acid synthase inhibition as a topical and systemic therapy for various pathogens is based on the fact that the fatty acid biosynthetic pathway in man is normally down regulated due to the high fat content in our diet. In man, significant fatty acid synthesis may occur in two sites: the liver, where free palmitic acid is the predominant product (Roncari, Can. J. Biochem., 52: 221-230, 1974); and lactating mammary glands where C.sub.10 -C.sub.14 fatty acids predominate (Thompson, et al., Pediatr. Res., 19: 139-143, 1985). Except for lactation, and cycling endometrium (Joyeux, et al., J. Clin. Endocrinol. Metab., 70: 1319-1324, 1990), the fatty acid biosynthetic pathway is of minor physiologic importance, since exogenous dietary lipid intake down-regulates the pathway in the liver and other organs (Weiss, et at., Biol. Chem. Hoppe-Seyler, 367: 905-912, 1986).
Since fatty acid synthesis occurs at insignificant levels in humans but at high levels in various pathogenic microorganisms, the fatty acid biosynthetic pathway thus provides a potential selective target for the development of antibiotic and antiparasitic therapies.